Just came across this pic and thought I'd read a few comments and saw this. You might be a while waiting for a reply from artgerm as this is an old post.

However... I would bet that after setting the line-art to multiply, you would freeze the transparency of the line-art layer ("lock transparent pixels" in photoshop for instance) and then you can paint over the top of the lines, picking darker/lighter colours, as appropriate, from the surrounding picture using the colour picker to get the right tint.

I'm guessing Artgerm does all his lineart by freehand (he is a master after all) but for those wanting to get them as smooth in Painter, here's one way how how:1. Select the pen tool with a 1px brush in a different colour you want the lineart to be, i.e. red.2. Then create the line using the pen (Painter will create a shape layer).3. When you're finished, create a layer above the shape layer and select the brush tool changing the colour to black. I prefer the Scratchboard Brush.4. Then on the tool bar at the top you'll see a brush icon with a semi-circle around it. This is the Align-To-Path tool. Click this! And voila! You can draw over your shape line/layer perfectly! Increase the brush size gradually so you can get it to have various thicknesses and tapering. 5. Delete the shape layer!

In Photoshop you can do the same by choosing the brush size you want, then selecting the pen tool, draw your path, then right-click, select stroke path and check the box saying simulate pressure